Lasers have been around in one form or another for the past fifty years. More recently, semiconductor materials have come to be employed as a lasing medium. In semiconductor lasers generally, the requisite population inversion is established by pumping excess ions into the conduction band. Stimulated emission—that is, lasing—occurs as the electrons fall across the band gap.
High power diode lasers are one form of semiconductor laser which convert electrical energy into laser emissions—that is, coherent light—at a relatively high efficiency, typically greater than 50%. Typical individual diode lasers are approximately 10 mm wide and approximately 0.1 mm high. While such diode lasers operating singly emit about 50 watts (W) of continuous output power, this output can be scaled upwardly into the kilowatt (kW) range by assembling individual diode lasers in a so-called stacked array.
Conventionally, a stacked array comprises several individual strips, or bars, of diode lasers arranged one on top of the other in the Y axis, with each bar in turn consisting of a linear series of individual diode lasers having their radiation-emitting openings arranged in a straight line and paralleling the same plane (X-Y) as the strips. A heat sink is commonly associated with each strip. In a typical diode laser array, individual diode lasers in a given strip are placed equidistant apart along a fixed-distance, for instance 10 mm. Each individual diode laser in the strip is characterized, typically, by a light emitting area of about 2.0 mm in the X axis, and about 0.001 in the Y axis. Typical divergence for these lasers is about 10 degrees full angle in the X axis, and about 90 degrees full angle in the Y axis. Thus, a single diode laser strip having a 10 mm width exhibits an emitting area of about 10 mm in the X axis and about 0.001 mm in the Y axis, with divergence of about 10 degrees in the X axis and about 90 degrees in the Y axis.
Their high conversion efficiency, as well as their relatively compact size and long operating life, make semiconductor lasers such as diode lasers an attractive choice for pumping-type solid-state lasers, such as Neodymium:Yttrium Aluminum Garnet (Nd:YAG) lasers, and for use in a variety of material processing applications, including, for example, surface heat treatment, laser cutting, laser welding, etc.
Despite their advantages, however, conventional diode lasers, particularly in the stacked array form, are characterized by limited beam quality and a highly asymmetric output beam. Importantly, these drawbacks prohibit focusing the laser output beam on a small focal point, a common requirement in material processing applications.
State of the art optical assemblies for symmetrizing the output beam and increasing brightness thereof employ refractive optical elements which section the output beam. This approach mandates very close manufacturing tolerances and precise assembly, in consequence of which such state of the art optical assemblies are high in cost.
It would therefore be desirable to provide for an optical assembly for shaping the output beam of one or more semiconductor lasers which is at once more economical to manufacture, and which overcomes other drawbacks found in conventional optical assemblies.